Vitamin D Deficiency Tied to ESRD in Blacks

Action Points

Explain to interested patients that low vitamin D levels have been associated with higher rates of end-stage renal disease among African-Americans.

Note the study found that low levels of vitamin D accounted for about 58% of cases of end-stage renal disease among blacks.

Vitamin D deficiency may account for a larger proportion of end-stage renal disease (ESRD) cases among African-Americans than among whites, according to a study adding to a growing body of evidence that the vitamin plays a key role in the progression of kidney disease and need for dialysis.

Non-Hispanic blacks were nearly three times more likely to eventually require dialysis than non-Hispanic whites (95% CI 1.03 to 7.77), an online article in the October 29 issue of the Journal of the American Society of Nephrology reported.

Meanwhile, low levels of 25-hydroxyvitamin D, known as 25(OH)D, accounted for about 58% of cases of ESRD among blacks (95% CI 0.38 to 8.21), the study found.

"The increased prevalence of 25(OH)D <15 ng/ml among non-Hispanic black individuals seems to explain a substantial proportion of their excess risk for ESRD," Michal L. Melamed, MD, of Albert Einstein College of Medicine, and colleagues wrote.

"These results need to be tested in future observational studies, and, if confirmed, then randomized, controlled trials evaluating the renoprotective effects of vitamin D supplementation may be warranted."

Most previous studies have shown that non-Hispanic blacks have a similar risk for milder stages of chronic kidney disease, but are at higher risk for ESRD, according to the researchers.

Earlier studies found an association between low levels of 25(OH)D and higher incidence of hypertension, insulin resistance, peripheral arterial disease, cardiovascular disease and mortality, and suggested it might affect the progression of renal disease.

Non-Hispanic blacks (and Hispanics) have lower levels of 25(OH)D than non-Hispanic whites, potentially because of darker skin that is less efficient at turning UVB rays from sunshine into vitamin D.

But no studies have found a link between low 25(OH)D levels and a variety of outcomes in blacks.

To explore whether low vitamin D could affect ESRD rates in African-Americans, Melamed and colleagues analyzed data from the Third National Health and Nutrition Examination Survey–linked Medicare claim files on 13,000 Americans.

The data included measurements of blood levels of 25(OH)D and incidence of ESRD.

They found that 34% of non-Hispanic black individuals had 25(OH)D levels less than 15 ng/ml compared with 5% of non-Hispanic white individuals (P<0.001).

The incidence rates of ESRD by race and ethnicity were:

198 (72 to 301) per 1,000,000 person-years for non-Hispanic whites

767 (498 to 1006) per 1,000,000 person-years for non-Hispanic blacks

387 (200 to 526) per 1,000,000 person-years for Mexican-Americans

After adjusting for demographic, socioeconomic, and clinical and laboratory factors, the researchers found that all participants with 25(OH)D levels less than 15 ng/ml had a 2.6-fold greater incidence of ESRD than those with levels of at least 15 ng/ml (95% 1.00 to 7.05; P=0.05).

They noted that the study was observational and could not infer that low vitamin D levels were a direct cause of the higher rates of ESRD.

They also cautioned that the data may not have reflected a subject's lifetime vitamin D status, since levels of the vitamin were tested once at the beginning of the study.

Since the study was based on small sample sizes, the authors considered it "hypothesis generating."

The study was funded by the National Institutes of Health and the American Heart Association.

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